Okay but like... Can you people not create 2 accounts and send a message from one another and see what happens (I don't use tumblr, so I can t try this out myself).
If you only have one device you should be able to replicate that using two different browsers (maybe put them in incognito mode).
If you only have one device you should be able to replicate that using two different browsers (maybe put them in incognito mode).